Scintillation detector package having radioactive support apparatus

ABSTRACT

A radiation detector package includes a support apparatus at least part of which is constructed from a naturally occurring radioactive material. A scintillator is associated with the support apparatus. The support may include a detector housing carrying a photodetector and the scintillator, and the detector housing may be constructed from the naturally occurring radioactive material.

FIELD OF THE DISCLOSURE

This disclosure related to the field of scintillators, and, moreparticularly, to scintillators that may be used in well logging or otherapplications.

BACKGROUND

Radiation detectors, such as gamma-ray or x-ray detectors, for example,often use a scintillator material which converts energy deposited by agiven type of radiation (e.g., gamma-rays or x-rays) into light. Thelight is directed to a photodetector, which converts the light generatedby the scintillator into an electrical signal, which may be used tomeasure the amount of radiation which is deposited in the crystal.

In the case of well-logging tools for hydrocarbon wells (e.g., gas andoil wells), a borehole radiation detector may be incorporated into thetool string to measure radiation from the geological formationsurrounding the borehole to determine information about the geologicalformation, including the location of gas and oil. The measured radiationmay be naturally occurring radiation emanating from the materials in andaround the hydrocarbon well, or may be radiation emanating from thematerials in and around the hydrocarbon well as a result of interactionswith radiation (e.g. neutrons, gamma-rays, or x-rays) radiated into thehydrocarbon well by the well-logging tool.

In some applications, it may be useful to gain stabilize a radiationdetector. As such, new developments in the area of radiation detectorsand ways to gain stabilize them are desirable.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

A radiation detector package may include a support apparatus at leastpart of which comprises a naturally occurring radioactive material, anda scintillator associated with the support apparatus.

A method apparatus is directed to a method of logging a formation havinga borehole therein. The method may include lowering a well logginginstrument into the borehole, and detecting incoming radiation from theformation using a radiation detector package carried by the well logginginstrument, the radiation detector package comprising a supportapparatus at least part of which comprises a naturally occurringradioactive material, and a scintillator associated with the supportapparatus. The method may further include gain stabilizing the radiationdetector package based upon detecting scintillations of the scintillatorcaused by radiation emitted by the naturally occurring radioactivematerial, using gain stabilization circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic block diagram of a radiation detector inaccordance with the present disclosure including a radioactivereflective material, wherein the scintillator and photodetector share acommon housing.

FIG. 1B is a schematic block diagram of a radiation detector inaccordance with the present disclosure including a radioactivereflective material, wherein the scintillator has its own housing.

FIG. 2 is a schematic block diagram of a radiation detector inaccordance with the present disclosure wherein the radioactivereflective material is at an end of the housing of the radiationdetector.

FIG. 3 is a schematic block diagram of radiation detector in accordancewith the present disclosure including both a radioactive reflectivematerial and a non-radioactive reflective material.

FIG. 4 is a schematic block diagram of radiation detector in accordancewith the present disclosure wherein the radioactive reflective materialis at least partially embedded in a sleeve surrounding the scintillator.

FIG. 5 is a schematic block diagram of radiation detector in accordancewith the present disclosure with a non-radioactive reflective materialat least partially surrounding the radioactive reflective material.

FIG. 6 is a schematic block diagram of radiation detector in accordancewith the present disclosure wherein an absorptive layer is between thescintillator and radioactive reflective material.

FIG. 7 is a schematic block diagram of a radiation detector inaccordance with the present disclosure wherein a naturally occurringradioactive material is between the housing and a reflective materialthat is adjacent the scintillator.

FIG. 8 is a schematic block diagram of a well-logging tool in which theradiation detectors disclosed herein may be used.

DETAILED DESCRIPTION

The present description is made with reference to the accompanyingdrawings, in which example embodiments are shown. However, manydifferent embodiments may be used, and thus the description should notbe construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete. Like numbers separated by century refer to like elementsthroughout, with the exception of those elements shown in FIG. 7.

Referring initially to FIG. 1A, a radiation detector 100 is nowdescribed. The radiation detector 100 includes a scintillator 110coupled to a photodetector 102 through an optical coupler 106 (e.g. asilicon pad, optical grease, etc.). The detector housing 108 in theillustrated example is cylindrical, such as typical for use in awell-logging tool, as will be described further below. The detectorhousing 108 may comprise a metal (e.g. aluminum, magnesium etc.), or aceramic, which allows radiation such as gamma rays, x-rays or neutronsto pass through. Alternatively, the housing 108 could be made of anon-metallic material such as a high strength carbon-fiber reinforcedpolymer. The scintillator 110 is pushed against the photodetector usinga spring 116. An optional base plate 114 may be between the scintillator110 and the spring 116. The photodetector 102 may include a photocathodeand a photomultiplier tube, the entrance window (not shown) of which iscoupled to the scintillation crystal with the optical coupler 106. Itshould be noted that other suitable photodetector 102 configurations maybe used in some applications, such as an avalanche photodiode (APD)configuration, or silicon photomultiplier configuration, for example.

The detector housing 108, base plate 114, spring 116, or any combinationthereof may be constructed at least partly from a naturally occurringradioactive material. For example, they may be constructed entirely fromthe naturally occurring radioactive material, or may be constructed froma non-radioactive substrate with the naturally occurring radioactivematerial therein or thereon, or may be constructed from a ceramic withthe naturally occurring radioactive material integrated therein. Theradioactivity of the naturally occurring radioactive material can beused to gain stabilize the radiation detector 100, as will be explainedbelow in detail.

Alternatively, the scintillator itself may be enclosed in its ownhousing as shown in FIG. 1B. This is to protect scintillators likeNaI(Tl), LaBr₃, etc. from deteriorating in the presence of humidity.Here, the scintillator may be hermetically sealed in its housing 122. Atone end of the housing 122 the scintillator 110 is coupled to an exitwindow 126 with an optical coupler 124. On the other end a spring 116pushes the scintillator 110 against the exit window 126. In turn, thescintillator housing is pushed against the photodetector by a spring128. There may be an optional base plate between the spring 116 and thescintillator 110.

Similarly to that described above, the housing 122, base plate, spring116, or any combination thereof may be constructed from a naturallyoccurring radioactive material. The naturally occurring radioactivematerial may be lutetium, potassium, thorium, lanthanum or anycombinations thereof, with or without other non-radioactive materialsincluded. The naturally occurring radioactive material may be an oxideof the materials listed above, for example Lu₂O₃ or La₂O₃. In fact, thenaturally occurring radioactive material may include any of thematerials listed above as well as oxides thereof.

In addition, the naturally occurring radioactive material may be ametallic substance in solid form, such as one of the listed materials,or a combination thereof. Additionally, the naturally occurringradioactive material may be one or more of the previous listed materialsin metallic form alloyed with a non-radioactive metal.

The scintillator 110 may be a plastic scintillator or crystalscintillator, for example. Indeed, various types of scintillatormaterials may be used for the scintillator 110 depending upon the givenapplication. Example scintillator materials may include: gadoliniumoxyorthosilicate (GSO), YAlO₃ (YAP), LuYAP, LaCl₃(Ce) (lanthanumchloride doped with Cerium), LaBr₃(Ce) (Cerium-doped lanthanum bromide),bismuth germanate (BGO), NaI(Tl), LuAG, YAG, LuAP, SrI₂, GAGG/GYGaGG,CeBr₃, GdI₂, LuI₂, ceramic scintillators, GPS, LPS, BaBrI, LuAG ceramic,LiCaF, CLYC, CLLB, CLLC, etc.

As noted above, scintillators are widely used in radiation detectors 100in several research and industrial fields, including the oil industry.The scintillator emits light when struck by ionizing radiation. In aradiation detector 100 configuration, the scintillation light is to bedirected towards the photodetector 102, whose function is to convert thelight signal into an electrical signal. The electrical signal may beamplified by an amplifier(s), which may provide an amplified signal to asignal processor or processing circuitry. The signal processor mayinclude a general or special-purpose processor, such as a microprocessoror field programmable gate array, and associated memory, and may performa spectroscopic analysis of the electrical signal, for example.

There is a radioactive reflective material 112 between at least aportion of the detector housing (108) or the scintillator packagehousing 122 and the scintillator 110. The reflective properties of theradioactive reflective material 112 helps improve light transport anddirect light emitted by the scintillator into the photodetector 102. Theradioactivity of the radioactive reflective material 112 can be used togain stabilize the radiation detector 100, as will be explained below indetail.

In addition, the exit window 126 may be constructed from anon-scintillating, radioactive material, and may also be used to gainstabilize the radiation detector. This non-scintillating, radioactivematerial may be naturally occurring, and may comprise lutetium, forexample. Indeed, the non-scintillating, radioactive material may beundoped LuAP or undoped LuAG, such as LuAP that is not doped with ceriumand LuAG that is not doped with cerium. The exit window could also bemade of Lu₂O₃ ceramic or could be a glass containing potassium, forexample. The radioactive reflective material 112 may be in powderedform, and may be a naturally occurring material. It should be noted thatthe radioactive reflective 112 material may be mixed with anon-radioactive reflective metallic powder, such as aluminum, silver, ora non-metallic powder such as Al₂O₃, or TiO₂. This may be done to reducethe radioactivity of the radioactive reflective powder and/or itsability to absorb incoming radiation from a formation.

The radioactive reflective material 112 may be any suitable material.Suitable materials are chemically compatible with typical scintillatormaterials (e.g. not cause degradation of optical parameters duringextended periods at high temperature), chemically stable at boreholetemperatures, emit radiation such as gamma-rays that form scintillationlines separate from the ones of interest in the measurement (usable forgain stabilization, as will be explained below), and emit sufficientamounts of radiation such that the statistical precision is adequate forgain stabilization but not so much that the material becomes a radiationhazard.

In accordance with this, the radioactive reflective material 112 maycomprise (i.e. be partially constituted from) lutetium, potassium,lanthanum, or thorium, and for example may be Lu₂O₃, KCl, ThO₂, LaO, orany mix thereof. Having the radioactive reflective material 112 be anaturally occurring material, as opposed to a material created in areactor or particle accelerator, can be useful in that the resultingradiation detector 100 may be subject to fewer government regulations.Thus, it should be understood that a naturally occurring material meansa material not created in a reactor or particle accelerator, and amaterial that has not been enriched to increase the fraction ofradioactive isotopes therein. Thus, a naturally occurring material isone with its naturally occurring isotopic distribution.

The radioactive reflective material 112 may be adjacent portions of thescintillator 110, or may surround the scintillator as in FIG. 1. Indeed,the radioactive reflective material 112 may be described ascircumscribing the scintillator 110 along a longitudinal axis thereof,and as well as an end of the scintillator.

In some applications, as shown in FIG. 2, the radioactive reflectivematerial 212 is adjacent an end of the scintillator 210 withoutpartially or fully circumscribing the longitudinal axis of thescintillator. In other applications, as shown in FIG. 3, the radioactivereflective material 312 may be adjacent a portion or portions of thescintillator 310, while a non-radioactive reflective material 318 may beadjacent another portion or portions of the scintillator. This may bedone to form a “window” to help allow certain energies and types ofexternal incoming radiation to more easily reach the scintillator 310.The radiation detector 310 can be oriented in a well logging instrumentsuch that the “window” faces a direction from which incoming radiationfrom a formation into which the well logging instrument is inserted islikely to be received. In some such applications, it would beparticularly useful if the non-radioactive reflective material 318 has asame reflectance as the radioactive reflective material 312, butattenuates radiation such as gamma rays less than the radioactivereflective material. As another approach, it could also be useful if thenon-radioactive reflective material 318 is less dense than theradioactive reflective material 312, so as to help enhance thedirectionality of the radiation sensitivity of the radiation detector310.

To help restrict the radioactive reflective material 412 from movingwithin the scintillator package housing 408, the radioactive reflectivematerial 412 may be completely or incompletely embedded in an elastomer,as shown in FIG. 4.

To help further improve light transport, in some cases, anon-radioactive reflective material 522, such as a reflective elastomeror Teflon, may partially or fully surround the radioactive reflectivematerial 512, as shown in FIG. 5.

As will now be explained with reference to FIG. 6, when the radioactivereflective material 612 emits radiation, that radiation may be in theform of alpha, beta, or gamma radiation. To shield the scintillator 610from undesirable forms of radiation, typically the alpha and betaradiation, there may be an absorptive layer 620 between the radioactivereflective material 612 and the scintillator to absorb the alpharadiation and/or beta radiation. This absorptive layer 620 is opticallytransparent, and may helpfully have a low index of refraction.

In a typical density measurement using a radiation generator, such as anelectronic radiation generator or a radioisotopic source, the radiationgenerated by the radiation generator and directed into a formationscatters many times before the byproducts of those scatteringinteractions reach the radiation detector 600. Thus, the radiationincoming to the radiation detector 600 from the formation may have anenergy of less than 300 keV. To gain stabilize the detector 600, a“check” source of radiation that produces radiation having an energygreater than that of the radiation incoming to the radiation detector,but not too much greater, is useful. The radioactive reflective material612 serves this purpose. When radiation from the radioactive reflectivematerial 612 strikes the scintillator 610, scintillation lines separatefrom those of interest in making the density measurement are detected.These detected scintillation lines can be used by gain stabilizationcircuitry 630 to gain stabilize the radiation detector 600.

In an application shown in FIG. 7, there is a non-radioactive reflectivematerial 713 at least partially surrounding the scintillator 710. Anaturally occurring radioactive material 723, such as a sleeve, at leastpartially surrounds the non-radioactive reflective material 713 to urgethe non-radioactive reflective material into the scintillator 710. Thisconfiguration works for situations where the scintillator 710 has itsown housing, as well as for situations where the scintillator andphotodetector 702 are in a common housing.

It should be noted that the scintillator packages and radiationdetection systems disclosed herein are suitable for uses outside ofoilfield applications, for example in the medical, mining, materialsinspection, and security fields.

Turning now to FIG. 8, an example of a well-logging tool in which one ormore radiation detectors 30 (similar to those described above) may beused. The detectors 30 are positioned within a sonde housing 918 alongwith a radiation generator 936 (e.g., neutron generator, x-raygenerator, etc.) and associated high voltage electrical components(e.g., power supply). In some applications, the detectors 30 andradiation generator 936 could be in a pad rather than a sonde.Supporting control circuitry 914 for the radiation generator 936 (e.g.,low voltage control components) and other components, such as downholetelemetry circuitry 912, may also be carried in the sonde housing 918.

The sonde housing 918 is to be moved through a borehole 920. In theillustrated example, the borehole 920 is lined with a steel casing 922and a surrounding cement annulus 924, although the sonde housing andradiation generator 936 may be used with other borehole configurations(e.g., open holes). By way of example, the sonde housing 918 may besuspended in the borehole 920 by a cable 926, although a coiled tubing,etc., may also be used. Furthermore, other modes of conveyance of thesonde housing 918 within the borehole 920 may be used, such as wireline,slickline, Tough Logging Conditions (TLC) systems, and logging whiledrilling (LWD), for example. The sonde housing 918 may also be deployedfor extended or permanent monitoring in some applications.

A multi-conductor power supply cable 930 may be carried by the cable 926to provide electrical power from the surface (from power supplycircuitry 932) downhole to the sonde housing 918 and the electricalcomponents therein (i.e., the downhole telemetry circuitry 912,low-voltage radiation generator support circuitry 914, and one or moreof the above-described radiation detectors 30). However, in otherconfigurations power may be supplied by batteries and/or a downholepower generator, for example.

The radiation generator 936 is operated to emit x-rays or otherradiation to irradiate the geological formation adjacent the sondehousing 918. X-rays or other radiation that returns from the formationare detected by the radiation detectors 30. The outputs of the radiationdetectors 30 are communicated to the surface via the downhole telemetrycircuitry 912 and the surface telemetry circuitry 932 and may beanalyzed by a signal analyzer 934 to obtain information regarding thegeological formation. By way of example, the signal analyzer 934 may beimplemented by a computer system executing signal analysis software forobtaining information regarding the formation. More particularly, oil,gas, water and other elements of the geological formation havedistinctive radiation signatures that permit identification of theseelements. Signal analysis can also be carried out downhole within thesonde housing 918 in some embodiments.

Many modifications and other embodiments will come to the mind of oneskilled in the art having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it isunderstood that various modifications and embodiments are intended to beincluded within the scope of the appended claims.

The invention claimed is:
 1. A radiation detector package for detectingfirst radiation incoming from outside of the radiation detector packageand second radiation from a naturally occurring radioactive materialfrom within the radiation detector package, the radiation detectorpackage comprising: a support apparatus at least part of which comprisesthe naturally occurring radioactive material; a scintillator at leastpartially supported in position by the support apparatus, wherein thesupport apparatus and the scintillator are configured to enable thescintillator to detect both the first radiation incoming from outside ofthe radiation detector package and the second radiation from thenaturally occurring radioactive material from within the radiationdetector package, wherein said support apparatus is configured to enablethe radiation detector package to sustain downhole drilling or loggingoperations; a photodetector optically connected with the scintillator;and a gain stabilization circuitry communicatively connected with thephotodetector, wherein the gain stabilization circuitry is operable togain stabilize the radiation detector package based on signals caused bythe second radiation detected by the scintillator.
 2. The radiationdetector package of claim 1, wherein the support apparatus comprises adetector housing carrying the photodetector and the scintillator; andwherein the detector housing comprises the naturally occurringradioactive material.
 3. The radiation detector package of claim 1,wherein the support apparatus comprises a scintillator housing carryingthe scintillator, and a detector housing carrying the photodetector andthe scintillator housing; and wherein the scintillator housing comprisesthe naturally occurring radioactive material.
 4. The radiation detectorpackage of claim 1, wherein the support apparatus comprises ascintillator housing carrying the scintillator, and a detector housingcarrying the photodetector and the scintillator housing; and wherein thedetector housing comprises the naturally occurring radioactive material.5. The radiation detector package of claim 1, wherein the supportapparatus comprises: a scintillator housing carrying the scintillatorand having first and second ends; a detector housing carrying thephotodetector and the scintillator housing, the photodetector beingadjacent the first end of the scintillator housing; a base plate in thedetector housing and adjacent the second end of the scintillatorhousing; a biasing member in the detector housing positioned such thatit urges the base plate toward the second end of the scintillatorhousing, thereby urging the scintillator housing toward thephotodetector; and wherein the base plate comprises the naturallyoccurring radioactive material.
 6. The radiation detector package ofclaim 1, wherein the support apparatus comprises: a scintillator housingcarrying the scintillator and having first and second ends; a detectorhousing carrying the photodetector and the scintillator housing, thephotodetector being adjacent the first end of the scintillator housing;a base plate in the detector housing and adjacent the second end of thescintillator housing; a biasing member in the detector housingpositioned such that it urges the base plate toward the second end ofthe scintillator housing, thereby urging the scintillator housing towardthe photodetector; and wherein the biasing member comprises thenaturally occurring radioactive material.
 7. The radiation detectorpackage of claim 1, wherein the support apparatus comprises: ascintillator housing carrying the scintillator and comprising atransparent window at an end thereof; a detector housing carrying thephotodetector and the scintillator housing; a base plate in thescintillator housing adjacent the scintillator and opposite thetransparent window; a biasing member in scintillator housing positionedsuch that it urges the base plate toward the scintillator, therebyurging the scintillator toward the transparent window; and wherein thebase plate comprises the naturally occurring radioactive material. 8.The radiation detector package of claim 1, wherein the support apparatuscomprises: a scintillator housing carrying the scintillator andcomprising a transparent window at an end thereof; a detector housingcarrying the photodetector and the scintillator housing; a base plate inthe scintillator housing adjacent the scintillator and opposite thetransparent window; a biasing member in scintillator housing positionedsuch that it urges the base plate toward the scintillator, therebyurging the scintillator toward the transparent window; and wherein thebiasing member comprises the naturally occurring radioactive material.9. The radiation detector package of claim 1, wherein the supportapparatus comprises: a detector housing carrying the photodetector andthe scintillator; a base plate in the detector housing adjacent thescintillator and opposite the photodetector; a biasing member in thedetector housing being positioned such that it urges the base platetoward the scintillator, thereby urging the scintillator toward thephotodetector; and wherein the base plate comprises the naturallyoccurring radioactive material.
 10. The radiation detector package ofclaim 1, wherein the support apparatus comprises: a detector housingcarrying the photodetector and the scintillator; a base plate in thedetector housing adjacent the scintillator and opposite thephotodetector; a biasing member in the detector housing being positionedsuch that it urges the base plate toward the scintillator, therebyurging the scintillator toward the photodetector; and wherein thebiasing member comprises the naturally occurring radioactive material.11. The radiation detector package of claim 1 further comprising ahousing disposed about the support apparatus and the scintillator,wherein the support apparatus comprises a sleeve between the housing andthe scintillator, and wherein the sleeve comprises the naturallyoccurring radioactive material.
 12. The radiation detector package ofclaim 1, wherein the naturally occurring radioactive material comprisesa metallic substance in solid form.
 13. The radiation detector packageof claim 1, wherein the naturally occurring radioactive materialcomprises a naturally occurring radioactive metal alloyed with at leastone non-radioactive metal.
 14. The radiation detector package of claim1, wherein the naturally occurring radioactive material is integrated inor on a non-radioactive substrate.
 15. The radiation detector package ofclaim 1, wherein the naturally occurring radioactive material isintegrated within a ceramic.
 16. The radiation detector package of claim1, wherein the naturally occurring radioactive material comprises atleast one radioactive oxide.
 17. The radiation detector package of claim1, wherein the naturally occurring radioactive material comprises Lu₂O₃.18. The radiation detector package of claim 1, wherein the naturallyoccurring radioactive material comprises lutetium and/or potassiumand/or thorium and/or lanthanum or combinations thereof.
 19. Theradiation detector package of claim 1, wherein the support apparatuscomprises a detector housing carrying the photodetector and thescintillator; and comprising a naturally radioactive reflective materialbetween at least a portion of the scintillator and the detector housing.20. The radiation detector package of claim 19, wherein the naturallyoccurring radioactive reflective material comprises lutetium and/orpotassium and/or thorium and/or lanthanum or combinations thereof. 21.The radiation detector package of claim 1, wherein the support apparatuscomprises a detector housing carrying the photodetector and thescintillator, a non-radioactive reflective material between the detectorhousing and scintillator, and a naturally occurring radioactive materialbetween the detector housing and non-radioactive reflective material.22. The radiation detector package of claim 1, wherein the supportapparatus comprises a scintillator housing carrying the scintillator,and a detector housing carrying the photodetector and the scintillatorhousing; and wherein the support apparatus comprises a non-radioactivereflective material between the scintillator housing and thescintillator, and a naturally occurring radioactive material between thescintillator housing and the non-radioactive reflective material. 23.The radiation detector package of claim 1, wherein the support apparatuscomprises a scintillator housing carrying the scintillator, and adetector housing carrying the photodetector and the scintillatorhousing; and comprising a naturally radioactive reflective materialbetween at least a portion of the scintillator and the scintillatorhousing.
 24. The radiation detector package of claim 23, wherein thenaturally occurring radioactive reflective material comprises lutetiumand/or potassium and/or thorium and/or lanthanum or combinationsthereof.
 25. The radiation detector package of claim 1, wherein thescintillator detects scintillation lines caused by the second radiationfrom the naturally occurring radioactive material, and wherein the gainstabilization circuitry gain stabilizes the radiation detector packagebased on the detected scintillation lines.
 26. The radiation detectorpackage of claim 1 not comprising another scintillator configured todetect the second radiation from the naturally occurring radioactivematerial of the support apparatus.